Obviously though those born blind will have to take it on good trust.
Not really, a deaf person can get evidence sound exists. There are ways of telling these things....
No. Whereas deaf people do have ways of telling that there is sound and even different kinds of sound, blind people cannot tell colour.
Helen Keller is well known for having confirmed this. For instance, she was even able to enjoy concerts and recitals, especially organ recitals, because she could feel the vibrations different sounds made, and could also sense rhythm. She readily distinguished between high and low sounds, and could even tell which instrument was playing. But she could not tell colour.
All her life she wanted to be able to distinguish colour, and frequently tried different methods to see if she had any degree of different sensation for different colours. She laid her hands on them, felt them, held them to her face, all manner of different methods, but although it was something she very, very much wanted to do, yearned to do, to her lifelong regret she was unable to distinguish any colour at all.
Now, Helen Keller is possibly the best example we could have for this. Not only had she no sight or hearing at all, but she was highly intelligent and very motivated to do learn and stretch herself way beyond what most people would ever think possible. She greatly advanced the understanding of what the deaf-blind are capable of, learning Braille and then more languages than most sighted or hearing people could ever master.
But it was a sorrow to her that colour eluded her.